1. Field of the Invention
The present invention relates to a band-feeding and tightening apparatus composed of at least a pair of rollers which are brought into compressive contact with each other through the intermediary of a band for retracting the strapping band against an article to be strapped after the band has been fed around the article to be strapped. The present invention relates in particular to a roller structure for tightening the band against the article to be strapped.
2. Description of the Prior Art
Band-feeding and tightening apparatuses composed of two or more pairs of rollers are conventional such as disclosed in U.S. Pat. No. 4,383,881 and Japanese Pat. No. 1,123,052.
As an example, means disclosed in Japanese Pat. No. 1,123,052 is illustrated in FIG. 4 and comprises a feed shaft 32 to which a feed roller 31 is fixed and a return shaft 34 to which a return roller 33 is fixed. Those shafts are caused to rotate at high speed in opposite directions relative to each other through the intermediary of a differential speed reducer. The band is fed into the strapping machine by bringing touch rollers 35a and 35b into compressively contact with the outer periphery of the feed roller 31; the primary tightening of the band is performed by bringing another touch roller 36 into compressively contact with the outer periphery of the return roller 33; and powerful secondary tightening is performed by means of a low-speed high-torque of the differential speed reducer by virtue of a crank connected to the return shaft 34 of the return roller 33, which crank starts to slide when the strength of tightening reaches a predetermined value thereby rapidly reducing the rotation of the return shaft 34.
The touch roller 36 is provided adjacent the lower surface of the return roller 33 to wind the band around the outer periphery of the return roller 33 whereby the contact area of the band with the return roller 33 is increased to prevent the band from slipping against the return roller 33 in the case of band tightening for performing firm tightening. When the band is fed by a high-speed feed roller 31 and when the band is fed by a return roller 33, the return roller 33 is also caused to reverse rotation at a high speed, such that the band is inevitably brought into contact with the return roller 33 which is reversely rotating which the band which is fed forwardly at a high speed. For this reason, the return roller 33 would wear out after a short period of time and could fuse to the band because of heat of friction between the return roller 33 and the band. There is a known disadvantage in that the band is jammed in an area between the outer periphery of the return roller 33 and the guide body 37 thereby making the band feeding impossible. It may occur that the touch roller 35a is brought into weak, compressive contact with the feed roller 31 and the touch roller 35b is brought into strong compressive with the feed roller 31 thereby preventing the contact of the band with return roller 33.
The above-described disadvantages may be regarded as being common to means provided with one or more roller pairs for retracting and tightening the band in addition to paired feed rollers for feeding the band. It has been learned that the disadvantages are mainly attributed to the outer periphery of the return roller 33 using a material or a shape to achieve high friction resistance for ensuring high torque, such as a metal on which a knurl is notched. Also, the disadvantages result from the fact that the feed rollers and the return roller caused to continuously rotate forward and reversely, respectively, for enhancing strapping efficiency. It is obvious that the band which is brought into contact with these rollers is subjected to high wear. Other problems result if the band slips off the rollers, and yet the presence of the guide body 37 to contain such a slipped band can itself result in a jamming of the band during normal band travel.